The present invention is related to liquid crystal materials for use in electro-optic applications. More particularly, many embodiments of the present invention relate to liquid crystal/polymer composite materials, and methods and apparatus for the manufacture and application of such composite materials.
Voltage imaging technology may be employed to detect and measure for defects in flat panel thin film transistor (herein after “TFT”) arrays. According to this measurement technique, the performance of a TFT array is simulated as if it were assembled into a TFT cell and then the characteristics of the TFT array are measured by indirectly measuring actual voltage distribution on the panel, or so-called voltage imaging, using an electro-optic (hereinafter “EO”) light modulator-based detector.
A voltage imaging optical system (hereinafter “VIOS”) in its most basic form includes an EO modulator, an imaging objective lens, a charge coupled device (CCD) camera or other appropriate or similar sensor, and an image processor. The electro-optic sensor of the EO modulator is based on the light scattering characteristics of liquid crystal (herein after “LC”) droplets in a polymer matrix, for example nematic liquid crystal droplets in a polymer matrix (liquid crystal/polymer composite, or LC/polymer) film. In prior operation, the EO modulator is placed approximately 5-75 microns above the surface of a TFT array, and a voltage bias is applied across a transparent electrode of a layer of indium tin oxide (hereinafter “ITO”) on a surface of the EO modulator. Thereupon, the EO modulator capacitively couples to the TFT array so that an electric field associated with the TFT array is sensed by the liquid crystal/polymer composite layer. The intensity of incident light transmitted through the LC/polymer layer is varied, i.e., is modulated, by any variations in the electric field strength across the liquid crystal (LC) material in the liquid crystal/polymer composite material. This light is then reflected off a dielectric mirror and collected by the CCD camera or like sensor. A source of incident radiation, which may be for example infrared or visible light, is provided so as to illuminate the LC/polymer film and dielectric mirror.
Due to the close proximity of components relative to panels under test (PUT), LC/polymer modulator structures can be subject to damage in normal use by unwanted particles, which can severely curtail the useful life. Thus, modulator lifetime improvement can be one of the major objectives in LC/polymer modulator research and development. For example, U.S. Pat. No. 7,817,333 discloses improved LC/polymer modulator structures. However, further improvements in switching voltage and gap distance without compromising mechanical properties of the LC modulator would be helpful.
Modulator sensitivity can be another important characteristic of an LC modulator device. Improved modulator sensitivity can lead to improved detection capability, and as such can be an important aspect of LC modulator development, in particular LC/polymer matrix research and development. Sensitivity for defect detection can be defined as the ratio of the change in transmitted light to the difference in voltage between a defective pixel and a good pixel on the TFT array. In addition, some applications such as LC displays for notebook computers and handheld devices can be sensitive to power consumption, such that prior displays having less than ideal sensitivity and higher than ideal voltages can lead to increased power consumption and decreased battery lifetime in at least some instances.
Work in relation with the present invention suggests that current LC materials and the current manufacturing testing methods associated therewith, may be less than ideal. For example, particulate contamination can damage test apparatus, for example a voltage imaging system and/or the panel under test. Also, test apparatus sensitivity may be less than ideal.
Polymer network liquid crystal (hereinafter “PNLC”) can be a morphology of polymer stabilized liquid crystal (hereinafter “PSLC”), and the prior PNLC and PSLC materials may not be well suited for use with voltage imaging systems in at least some instances. For example, these prior materials may lack intrinsic mechanical strength and film hardness due to their low percentage of polymer, for example less than 10% in at least some instances. Although interfacial polymerization has been used to encapsulate liquid crystal and prepolymer mixture, such prior interfacial polymerization can be somewhat cumbersome and can provide a less than ideal LC material in at least some instances. For example, interfacial polymerization can produce a highly cross-linked hard shell layer, and such a cross-linked shell layer can undesirably affect the switching of liquid crystal contained within the shell.
While the above materials, apparatus and methods may be suitable for certain applications, there is a need in the art for improved electro-optic LC materials, more specifically improved sensitivity and life-time performance of electro-optic LC materials and test apparatus.